Where do bitter substances in coffee come from?
Bitterness in coffee: briefly explained (bitter substances vs. acids vs. astringency)
Bitterness is a basic taste, acidity is lively and fruity, astringency feels dry and rough. A balanced cup combines sweetness, moderate acidity, and subtle bitterness. When coffee turns bitter, we often ask: Why does coffee taste bitter? It’s usually due to the roast profile or over-extraction.
Where do bitter substances come from during roasting? Maillard, protein degradation, and carbohydrates
During the Maillard reaction, aroma complexes and melanoidins are formed. In parallel, proteins break down and carbohydrates dehydrate, forming bitter substances. In very dark roasts, chlorogenic acid lactones, among others, are converted into more bitter phenylindanes. Good roasters balance development so that bitter substances do not dominate the coffee.
Too fast vs. too hot roasted: typical errors and why they enhance bitterness
Too fast: underdeveloped inside, harsh-bitter, grassy. Too hot: scorching/tipping, burnt, "ashy" tone on the surface. Both emphasize harsh bitterness and overshadow sweetness.
Bitterness during brewing: over-extraction as the most common trigger
Coffee over-extraction occurs due to grinding too fine, water too hot, brewing too long, or too much stirring. Late, bitter, and dry components dissolve disproportionately. Channeling yields paradoxical cups: simultaneously sour and bitter - typical for bitter espresso.
Practical check: How to reduce bitterness in espresso, filter, and automatic machines
- Espresso: Grind coarser, 1-2 °C cooler, improve flow (WDT/tamper), adjust recipe (e.g., 1:2 instead of 1:1.8).
- Filter: Slightly coarser, 92-94 °C, flow rate 2:30-3:30, stir moderately. Prevents bitter filter coffee.
- Automatic machine: Reduce temperature/"strength," adjust grind size, keep clean, use a medium roast.
Troubleshooting by symptom: bitter, burnt, dry, "ashy"
- Bitter: Over-extraction; coarser grind, cooler water, shorter brewing time.
- Burnt: Brewed too hot or roasted too dark/scorched; lower temperature, lighter roast.
- Dry/astringent: Water too hard, long contact time, old beans; fix water softness/time.
- "Ashy": Very dark, old coffee, dirty grinder; fresh, lighter, clean.
Specialty approach: how lighter roasts, water, and recipe parameters interact
Lighter roasts provide more clarity and less harsh bitterness. Water with moderate hardness and low alkalinity helps support sweetness and acidity. Fine-tuning grind size, temperature, and ratio – that’s the answer to “coffee too bitter, what to do?”
FAQ
Where do bitter substances in coffee come from?
Bitter substances are formed during roasting through heat-induced protein degradation and dehydration of carbohydrates – both occur before and during the Maillard reaction. If the coffee is too bitter, it was usually roasted too quickly (bitter substances were not fully broken down) or roasted too hot (combustion reactions on the bean surface). Over-extraction during brewing also creates bitterness – this is a more common mistake than poor roasting.
What helps immediately against bitter espresso?
Grind coarser (shorten extraction time), slightly lower the temperature, possibly reduce the dose or adjust the yield. Also check for channeling: uneven extraction makes espresso simultaneously sour and bitter.
Why does filter coffee taste bitter, even though the beans are high quality?
With filter coffee, over-extraction is particularly common: grind too fine, flow too slow, water too hot, or kept warm for too long. Water that is too hard can also intensify bitterness and dryness.
Further reading: Understanding extraction (Brew Control Chart), water chemistry for coffee, roast profiles and development time.
